US 7694513 B2
A wave power apparatus includes a plurality of rotationally supported arms, each of which carries a float (124) at its free end, so that a translational movement of the float caused by a wave results in rotation of the arm. The apparatus comprises power conversion means for converting power transmitted from the wave to the arms into electric power, e.g. a hydraulic system, in which a hydraulic fluid is displaced by the movement of the arms to drive one or more hydraulic motors. The plurality of are arranged in a row such that a wave passing the row of arms causes the arms to successively pivot with a mutual phase shift. Thereby, an even power output may be achieved, and the need for frequency converters may be reduced or eliminated. Preferably, each arm is connected to a hydraulic cylinder of the hydraulic system, whereby a plurality of arms feed hydraulic medium into the hydraulic motor or motors through common hydraulic conduits.
1. A wave power apparatus comprising:
a plurality of arms, each of which is rotationally supported at one end by a shaft, and wherein each arm carries a float at its other end, which is opposite to the supported end, so that a translational movement of the float caused by a wave results in rotation of the arm around the shaft,
a power converter that converts power transmitted from the wave to the arms into electric power, the plurality of arms being arranged in a row such that a wave passing the row of arms causes the arms to successively pivot around the shaft, the arms being arranged at mutual distances, so that the passage of the wave causes the arms to pivot with a mutual phase shift, the power converter comprising a hydraulic driving system with a hydraulically driven motor,
wherein each arm is connected to the hydraulic driving system by means of at least one hydraulic cylinder which causes a hydraulic medium of the hydraulic driving system to be displaced into the motor, the cylinders being arranged to displace the hydraulic medium to the motor via common hydraulic conduits,
wherein each cylinder is provided with a sensor for determining a position and/or rate of movement of the cylinder's piston, the sensor being arranged to transmit a signal to a control unit of the cylinders and associated valves, the sensors being configured to monitor the power output of each individual cylinder, so that the transmission of power from each individual cylinder to the motor via the common hydraulic conduits of the hydraulic driving system is individually controllable in response to the signal representing the individual cylinder's piston's position and/or rate of movement; and
wherein said control unit is configured to control the power output of each of the individual cylinders in such a manner that the power output of the apparatus is kept substantially even.
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The present invention relates to a wave power apparatus for converting power of sea or ocean waves into useful energy, such as electricity. The apparatus according to the invention specifically aims at providing a system, in which an even power output may be achieved.
It is well known that sea waves appear to constitute a nearly unlimited resource of energy which, if exploited efficiently, may possibly solve a significant proportion of the world's energy problems. However, despite of many attempts to exploit sea-wave energy, no commercially successful system for converting sea wave energy into electrical power has been devised so far.
In general, three different types of wave power apparatuses have been proposed in the prior art. One such apparatus is disclosed in U.S. Pat. No. 6,476,511, the apparatus comprising a plurality of buoyant cylindrical body members connected together at their ends to form an articulated chain-like structure. Each pair of adjacent cylindrical members is connected to each other by a coupling member, which permits relative rotational movement of the cylindrical members about a transverse axis. Adjacent coupling members may permit relative rotation about mutually orthogonal transverse axes. Each coupling member is provided with elements, such as a set of hydraulic rams, which resist and extract power from the relative rotational movement of the body members. The apparatus floats freely in the sea surface and is moored to the sea floor.
A second type of wave power apparatus comprises one or more surface floats capable of moving along the surface of the sea under the action of waves, and a reference member, which is fully submerged in the sea at a certain depth, and which is substantially unaffected by the waves, cf. for example U.S. Pat. No. 4,453,894. The movement of the float in the surface of the sea causes the displacement of a hydraulic fluid in a hydraulic system comprising hydraulic devices which interconnect the surface float or floats and the reference member, whereby useful energy may be extracted from the hydraulic system. It will be appreciated that this apparatus is also moored to the sea floor.
Finally, a third type of wave power apparatus is one having one or more arms supported by a supporting structure carrying one or more floats which are caused to move by the waves. The energy of moving waves transmitted into the arms and may be conveyed into a hydraulic system, as in the system of U.S. Pat. No. 4,013,382, or into a mechanical system of shafts which, via a mechanical transmission system, drive one or more electric generators for the production of electricity, as in the system of WO 01/92644.
The present invention is generally concerned with the third type of wave power apparatuses mentioned above. It is an object of preferred embodiments of the invention to provide an apparatus, which allows for an even power output of power conversion means of the apparatus, i.e. a power output which is substantially constant over time. It is a further object of preferred embodiments to provide a system which reduces or eliminates the need for frequency converters. It is a further object of preferred embodiments to provide a wave power apparatus which may conveniently be taken out of operation, e.g. to prevent formation of ice on various parts of the apparatus during operation. It is a still further object of preferred embodiments of the invention to provide an apparatus, which allows for convenient maintenance access to arms and floats, most preferably to allow for maintenance access of individual arms and floats in systems comprising a plurality of arms, each provided with a float. It is a still further object of preferred embodiments to provide an apparatus which may conveniently be conveyed from an on-shore production facility to the operational site at the open sea.
The present invention provides a wave power apparatus comprising a plurality of arms, each of which is rotationally supported at one end by a shaft, and wherein each arm carries a float at its other end, which is opposite to the supported end, so that a translational movement of the float caused by a wave results in rotation of the arm around the shaft, the apparatus comprising power conversion means for converting power transmitted from the wave to the arms into electric power, the plurality of arms being arranged in a row such that a wave passing the row of arms causes the arms to successively pivot around the shaft, the arms being arranged at mutual distances, so that the passage of the wave causes the arms to pivot with a mutual phase shift.
The arms are preferably arranged at mutual distances, so that at all times at least two of the arms simultaneously deliver a power contribute to the power conversion means. The power conversion means preferably comprise a hydraulic actuator associated with each arm, the hydraulic actuators feeding a hydraulic medium into at least one hydraulic motor via shared hydraulic conduits. Accordingly, an even power output of the power conversion means may be achieved. This is in particular the case in embodiments of the apparatus comprising a large number of arms, floats and actuators, e.g. 60, as the sum of the power contributes of the individual actuators is essentially constant over time. Possible pressure ripples on the pressure side of the hydraulic motor may be essentially eliminated by means of a spike suppression device which is known per se, the spike suppression device being arranged in fluid communication with the shared hydraulic conduits. Preferably, the sum of all power contributes is essentially constant at a certain wave climate, i.e. wave height and wave frequency. The hydraulic motor is preferably a hydraulic motor with variable displacement volume per revolution. Changes in the wave climate may be compensated by means of a control circuit which controls the displacement volume per revolution of the motor in order to keep the rpm of the motor essentially constant. In order to generate alternating current at a given frequency without utilizing a frequency converter, the rpm of the motor should be controllable within +/−0.1-0.2%. In case a different type of hydraulic motor is applied or in case the rpm is not controlled exactly, a frequency controller may be employed for fine-adjustment of the frequency of the AC current generated.
In preferred embodiments, the apparatus of the present invention comprises at least 5 arms, such as at least 20 arms, preferably at least 40 arms, preferably 50-80 arms, such as 55-65 arms, e.g. 60 arms. The arms of the apparatus are preferably distributed, such that there is provided at least five arms, preferably at least 10 arms, per wavelength of the ocean waves. At the open sea, the wave length of the ocean waves is typically 50-300 m, such as 50-200 m. In protected waters, the wave length of waves is typically 5-50 m.
In preferred embodiments, the apparatus spans over at least two wave lengths. This brings about the possibility to arrange a row of arms and floats at a relatively large angle with respect to the wave heading, e.g. at +/−60°, as the wave length projected onto the orientation of the row of floats spans over at least 2× cos(60°) wavelengths, i.e. at least one wavelength, whereby it is ensured that a power contribute is delivered at all times.
The plurality of arms are preferably arranged in one or more rows, e.g. in a star, V or hexagon formation as disclosed in WO 01/92644. In order to efficiently exploit the wave energy, the row of arms is preferably oriented such with respect to the wave heading that the row forms an angle of within +/−60° with respect to the wave heading.
It has been found that the efficiency of the apparatus according to the invention increases with increasing buoyancy of the float with regard to its dry weight. Accordingly, in preferred embodiments of the invention, the buoyancy of the float is at least 10 times its dry weight, such as at least 20, 30 or 50 times, preferably 20-40 times. For example, the dry weight of a float is typically 100 kg or less pr. meter cube of buoyancy, the buoyancy of salt water being typically approximately 1050 kg/m3. A float is typically made from hard low weight foam materials or balsa wood, which are coated with a composite, such as reinforced glass fiber composites or a combination of glass fiber and carbon fiber composites. Alternatively, a float may be made from a sandwich layer of reinforced fiber materiel with hard foam being provided in the middle of the sandwich and at the bottom and at the top of the float, with the foam layers being separated by a honeycomb structure of reinforced fiber materials.
Efficiency also increases with increasing diameter of the float relative to its height. Preferably, the diameter of the float is at least 5 times its height, such as at least 7 times, such as at least 10 times, or 5-20 times. In preferred embodiments, the float has an essentially circular cross-section, and in order to improve fluid dynamical properties of the float, it may have a rounded edge portion, which acts as a streamlining.
The power conversion means preferably comprise a hydraulic driving system with a hydraulically driven motor. For example, each arm may be connected to the hydraulic driving system by means of at least one actuator which causes a hydraulic medium of the hydraulic driving system to be displaced into a hydraulic motor, the actuator(s) being arranged to displace the hydraulic medium to the motor via hydraulic conduits. In case of several arms and several actuators, the hydraulic medium is preferably displaced to the motor via shared hydraulic conduits. In other words, several hydraulic actuators may feed hydraulic medium into one single hydraulic motor via a shared system of hydraulic conduits. Most preferably, the hydraulic medium is not accumulated in a hydraulic storage tank for accumulating hydraulic medium under pressure, from which pressure is released to the motor. Accordingly, the actuators feed hydraulic medium directly into the hydraulic motor. However, as discussed below, a battery of hydraulic accumulators may advantageously be applied for an entirely different purpose, i.e. for forcing a float into a wave near a wave trough. As in preferred embodiments, a plurality of actuators simultaneously transmit power to the motor, there is no need for a hydraulic storage tank, as the motor will be capable of running at a substantially constant speed and at a substantially constant power input thanks to the delivery of power in the shared hydraulic system from a plurality of actuators at a time.
It should be understood that there may be foreseen more than one single hydraulic motor. Preferably, two, three or more motors may be arranged in parallel at the end of the shared hydraulic conduit. Thus, the power delivered through the shared hydraulic conduit may drive several motors. If, for example the hydraulic driving system produces 4 MW, eight motors delivering 500 kW each may be coupled in parallel at the shared hydraulic conduit. The motors may deliver the same nominal power output, or they may deliver different nominal power outputs. For example, one motor may deliver 400 kW, one may deliver 500 kW, etc.
All hydraulic motors may also be linked through the same through-going shaft, which drives at least one common electric generator, or all hydraulic motors may drive one cog wheel which drives at least one common electric generator
In order to allow the hydraulic system to force the arm(s) and float(s) in any desired direction, each actuator may comprise a double-acting cylinder which may be used to extract energy from the arm into the hydraulic system and to feed energy from the hydraulic system into the arm, e.g. to drive the float into a wave near a wave trough as explained in detail below in connection with the hydraulic accumulators.
In preferred embodiments, the apparatus comprises means for forcing the float(s) into the waves at wave troughs, so as to increase the vertical distance traveled by the float to increase the power output in a wave cycle. Such means may e.g. comprise one or more hydraulic accumulators for intermittently storing energy in the hydraulic driving system. The energy stored in the hydraulic accumulators may advantageously be derived from the release of potential energy as the float is taken out of the water a wave crest. In other words, as a float moves from a submerged position in a wave near a wave crest to a position above water, potential energy is released. This energy may be accumulated in the accumulator or in a battery of accumulators, wherein different accumulators are charged at different pressures, e.g. at pressure steps according to the number of accumulators. In embodiments incorporating such hydraulic accumulators, the hydraulic driving system may be controllable to release the energy stored in the accumulator(s), when a float is passed by a wave trough, so as to drive the float carried by the arm into the wave. To improve the efficiency of the accumulator system, there may be employed a plurality of accumulators, such as at least 2, such as 3-20, such as typically 6-12, which preferably store hydraulic medium at different pressure steps. In preferred embodiments, the float is driven a certain distance into the wave near a wave trough, and subsequently the float is allowed to move upwardly in the wave, but yet submerged in the wave, and at the wave crest the float is released, i.e. allowed to move out of the water. As described above, the energy released as the float is released at the wave crest is used to charge the one or more hydraulic accumulators, at which energy is stored for driving the float into the wave. Accordingly, the potential energy released as the float moves out of the wave near the wave crest is not lost. On the contrary, it is utilized for driving the float into the wave at the wave trough, whereby the total vertical distance traveled by the float is increased. Consequently, the power output of a wave cycle is increased. It is estimated that, at a wave height of 1.5 m, the vertical distance traveled by the float may be increased from approximately 0.75 m to approximately 1.5 m, thus doubling the power output. The energy utilized to drive the float into the wave at the wave trough causes essentially no loss in the driving system, as the energy is provided by the release of the float at the wave crest.
In order to allow for accurate control of the system, each cylinder, or at least selected ones of the cylinders, may be provided with a sensor for determining a position and/or rate of movement of the cylinder's piston, the sensor being arranged to transmit a signal to a control unit of the cylinders and associated valves, so that the transmission of energy from the individual cylinders to the remaining parts of the hydraulic driving system is individually controllable in response to the signal representing the individual cylinder's piston's position and/or rate of movement. Thus, the cylinders may be individually controllable, and a cylinder may be withdrawn from operation, e.g. for maintenance, while the remaining cylinders keep operating, so that the entire system will be essentially unaffected by the withdrawal of a single cylinder. The sensor is preferably also utilized to control the depressing of the float into the water, i.e. to control release of pressure of the battery of accumulators as described above. The sensor may further be utilized to control charging of the accumulators, i.e. to determine the passage of a wave crest. Moreover, the sensor is useful to control releasing of the float at a wave crest, i.e. to prevent a catapult-like shoot-out of the float. The sensor may also be used for monitoring the power output of each individual actuator in the hydraulic driving system, so that the power output of the individual actuators and the entire apparatus as such may be optimized.
Whereas some prior art systems rely on submerged reference members for supporting those means which convert sea wave power into useful power or on shore-supports, it has been found that wave energy is most efficiently exploited on the open sea. Accordingly, the apparatus of the invention preferably comprises a supporting structure which is fixed to the sea floor. In a presently preferred embodiment, the supporting structure is fixed to the sea floor by means of a suction anchor, or alternatively by a gravity foundation, or fixed to a rocky seabed with studs. The supporting structure may advantageously comprise a truss structure, with the suction anchor being arranged at a first nodal point of the structure. At least one arm and preferably all arms of the apparatus are supported at second nodal points of the truss structure, most preferably at a summit of a triangular substructure of the truss structure. The triangular substructure may define two vertices at the sea floor, with a means for attaching the structure to the sea floor in each of the corners. Preferably, the means for attaching are at least partially embedded in the sea floor, e.g. under by gravity foundation or a suction anchor. As the means for attaching are arranged at the nodal points of the truss structure, vertical forces in the truss structure caused by the buoyancy of the floats may efficiently be counteracted. A truss structure as described above ensures a maximum degree of stability of the system while allowing for a low overall weight of the supporting structure.
It has been found that one general problem in prior art systems is to prevent extreme impacts occurring during storms and hurricanes from damaging the floats, arms and other parts of the wave power apparatuses. Embodiments of the present invention therefore provide features which makes it possible for the wave power apparatus to withstand extreme sea wave conditions. Such embodiment comprise a hydraulic lifting system for lifting the float out of the ocean and for locking the float in an upper position above the ocean surface.
The hydraulic lifting system preferably comprises one or more pumps for pumping hydraulic medium into the cylinders for lifting them out of the ocean.
Thanks to the hydraulic lifting system, the float may be withdrawn from the ocean and kept in a locked position above the ocean surface at the occurrence of e.g. storm or prior to the occurrence of icing. Thus, the only impact on the float when it is withdrawn from the ocean is the impact of wind, the forces of which are significantly smaller than the forces of waves. In one embodiment, the arms may be lifted out of the water by generating a hydraulic pressure in the hydraulic lifting system, which causes the arms to be displaced out of the ocean, and by appropriately shutting a valve, preferably by means of a conical locking pin, so as to maintain the lifting pressure. The hydraulic lifting system may be controlled from a remote on-shore location, or by a control system which forms part of the wave power machine, and which acts in response to a signal indicative of a stormy condition, e.g. to a signal from an electronic device for continuously determining the velocity of wind. The control system may be programmed to withdraw the float and arm from the water at a predetermined wave height. For example, this wave height may be a certain fraction, e.g. 30%, of the largest predicted wave referred to the operation site of the apparatus, the so-called “100-year wave”. At an ocean depth of 20 m, this height is approximately 18 m, and the control system accordingly takes the float and arm out of the ocean at a wave height of approximately 6 m. The wave height may be determined by a mechanical, optical, electro magnetic or acoustical system, e.g. a pressure transducer system with a pressure transducer arranged on the sea floor, an echo sound system arranged at the floats, an echo sound system arranged on a fixed supporting structure of the apparatus and pointing upwards towards the surface of the waves, or operating in air pointing downwards toward the water surface, or a sensor system with light transmitting or light receiving means arranged on the floats and/or on the fixed supporting structure, such light being, e.g., laser light. Alternatively, there may be provided a radar system at the structure. The pressure of a hydraulic medium in the lifting system may be generated by a pump forming part of the hydraulic lifting system. Alternatively, the pressure may be generated by releasing pressurised hydraulic medium from an appropriate hydraulic accumulator. The accumulator may e.g. be charged by a hydraulic driving system which, in one embodiment of the invention, is comprised in the power conversion means. For example, the accumulator for delivering the hydraulic lifting pressure may be an accumulator, or a plurality of accumulators in a so-called accumulator battery, for forcing the float into the wave at a wave trough as described in detail below.
The hydraulic lifting system is preferably adapted to individually lift each float out of the ocean. For example, the lifting system may comprise a plurality of hydraulic circuits, each of which is associated with one of the arms, and each of which comprises valve and/or pump means for pressurising the hydraulic circuit for lifting the arm and float out of the ocean. In one embodiment the hydraulic lifting system comprises fewer pumps than circuits, so that the or each pump is connected to a plurality of circuits, each circuit with associated valves being designated to one arm. In preferred embodiments of the invention, the power conversion means and the arms are arranged such that those arms, which are kept in the ocean, may deliver power to the power conversion means, while one or more other arms are kept lifted out of the ocean. Embodiments incorporating the power conversion means of WO 01/92644, which is hereby incorporated by reference, may allow for free-wheeling, around a driving shaft of the power conversion means, of arms which are lifted out of the ocean. Embodiments relying on hydraulic power conversion means, in which movement of the arms generates pressure in a hydraulic driving system, may comprise means for taking out of operation those power conversion means, e.g. those hydraulic actuators, which are associated with an arm, which has been lifted out of the ocean. In a presently preferred embodiment, an arm may be lifted out of the ocean and locked in an elevated position by the arm's actuator, e.g. a double-acting cylinder, which may be used to lift and lock the arm.
Preferred embodiments of the present invention also provide a solution to the problem of providing a stable rotational support of the arm or arms, which is less vulnerable to horizontal force components. It has been found that the structure of U.S. Pat. No. 4,013,382 is likely to become unstable due to horizontal force components generated by waves. More specifically, the bearings of the connecting rods are constituted by simple pins, and any slight slack in such bearings might cause irreparable damage to the connecting rods and their support. The apparatus of U.S. Pat. No. 4,013,382 is therefore unsuitable for installation at the open sea, i.e. at relatively large wave forces. The structure disclosed in WO 01/02644 also suffers from the disadvantage that even the slightest slack in the one-way bearings which support the rocker arms and which connect the rocker arm pipes and the force shaft might damage the bearings. Moreover, the apparatus of WO 01/02644, in which a total of some 40 rocker arms are supported by one single force shaft, requires an immensely strong force shaft which, due to its dimensions required in order for it to be able to transmit the required power, would be unfeasible due to its weight conferred by its large dimensions, such large dimensions being necessary due to the momentum transmitted from the arms to the force shaft. Preferred embodiments of the apparatus according to the present invention provide an improved support of the arms which makes the apparatus less vulnerable to horizontal force components. Therefore, in a preferred embodiment, the apparatus of the invention comprises a pair of pre-stressed and essentially slack-free bearings. The bearings are thus capable of efficiently counteracting radial and axial forces and consequently to withstand horizontal force components conferred by waves. The term “slack-free bearing” should be understood to comprise any bearing, which is slack-free in a horizontal and axial direction. For example, the pair of bearings may comprise two conical bearings with their conical faces being opposite to each other. In one embodiment, the bearings are pressure-lubricated.
In another embodiment, the bearing comprises an inner and an outer ring or cylinder, the inner ring being secured to a rotational shaft of the arm, and the outer ring being secured to a fixed support, the bearing further comprising a flexible material between the inner and the outer ring. During operation, the inner ring rotates relative to the outer ring, thereby twisting the flexible material. In order to adjust the stiffness of the flexible material, there may be provided at least one cavity or perforation in the material. The flexible material may, e.g., comprise a spring member, such as a flat spring. By appropriate positioning of the perforation(s) or by appropriate design of the spring member(s), the bearing support may be designed to have a larger force-bearing capacity in one direction than in another direction.
The arm is preferably supported by the bearings at two mounting points which are offset from a centre axis of the arm, the centre axis of the bearings being coincident with an axis of rotation of the arms. As each arm is connected to and supported by individual bearings, a stable rotational support for the arms is achieved. In particular, as the two bearings are preferably arranged at a mutual distance along the axis of rotation of the arm, an impact at the axis resulting from a horizontal force component on the float may be counteracted.
It will, accordingly, be appreciated that the structure of the present apparatus is more stable than the structure of prior art devices. As the present apparatus is primarily intended as an off-shore construction, stability is a major concern due to costs of maintenance at off-shore sites. Maintenance costs at off-shore sites are typically on average 10 times higher than maintenance costs at on-shore sites.
Preferred embodiments of the invention will now be further described with reference to the drawings, in which:
The below description of the drawings discloses a variety of features and options comprised in various embodiments of the wave power apparatus according to the invention. The operating principles of the broadest aspect of the invention will be appreciated best from the description of the embodiments of FIGS. 1 and 14-20.
The third, fourth, fifth and sixth nodal points 116,117, 118,120 are provided above the surface of the sea at a height sufficient to ensure that they are also above the sea surface when waves are high under stormy conditions. For example, the nodal points 116, 117, 118 and 120 may be provided at 20 meters above the surface of the sea when the sea is smooth. In order to transform the energy of the waves into hydraulic energy, the wave power apparatus 102 comprises a plurality of arms 122, each of which at one end comprises a float 124 and at the opposite end is connected to a shaft 126. The arms are adapted to rotate around the shafts 126. Each arm 122 is attached to a hydraulic actuator, such as a hydraulic cylinder 128 comprising a piston 130. The hydraulic cylinder 128 is pivotally connected to the arm in a first attachment point 132 and to the truss structure 104 in a second attachment point 134. The second attachment point is preferably located at a nodal point, i.e. along an edge portion of an essentially rectangular structure arranged on top of the triangular main structure of the truss structure. The floats 124 move the arms up- and downwardly influenced by the movement of the waves. When the arms move upwardly and downwardly, the piston 130 is moved, and thus the wave energy is transformed into hydraulic energy which may be converted into useful electric energy as described below in connection with
As shown in
As shown in
In order to provide an essentially maintenance-free bearing support for the rotation of the arms 122, the present inventors have proposed bearings as those shown in
Similar wriggle bearings 346, 348 and 354 are shown in
The inner and outer rings 145, 147 of
The bearing principles of
In the hydraulic diagram of
In each of the cylinders 128, the piston 130 divides the cylinder in upper and lower chambers 192, 194 which are interconnected via conduits 196 and 198. In each of the conduits 196 there is provided a two-way valve 200, and in parallel thereto there is provided, in conduit 198, a pressure valve 202 and a series flow control valve 204. Finally, each cylinder is provided with a control element 206 for determining the position and/or rate of movement of the piston 130 of the cylinder 128.
When the two-way valve 200 is open, the piston 130 may move freely when the arms 122 (see
It will be appreciated that, due to the large number of cylinders 128, it is at all times ensured that at least two of them, and preferably several, deliver a flow of hydraulic medium to the motor 182. Thereby, an even power output from the generator 184 may be ensured, preferably without any need for frequency converters.
The above description of
The system of
When an arm is to be lifted out of the water, valve 278, valve 286 and valve 288 shut. Valve 274 and 280 open, and the pump 268 may force hydraulic medium into the lower cylinder chamber 194, and the arm associated to the cylinder in question is elevated. Hydraulic medium in the upper cylinder chamber 192 is conducted to the reservoir 186 via valve 280. The control element 206 detects that the arm and with it the piston 130 has reached its desired position, e.g. its uppermost position, and a signal is passed to valves 274 and 280 causing them to shut. The piston 130 is consequently locked, and the arm is secured in a position, in which the float 124 is lifted out of the water. The arm 122 may be further supported by a pawl (not shown) engaging the arm.
In designing the system the typical wave length and directions of the location should be taken into account in order to ensure a substantially constant hydraulic pressure in the system. In preferred embodiments of the invention, the relationship between the wave direction (angle θ) and the length of the wave power apparatus, i.e. the length spanned by the floats 124, 164, may be determined by the following formula:
In the upper part of
In order to increase the power output of the wave power apparatus it is thus desirable to increase the vertical travel distance of the float 124. The lower part of
Evidently, a net gain in terms of overall power output of the wave power apparatus arises only if the power utilized for forcing the float 124 into the wave at the wave trough 152 is not deducted from the power output of the apparatus.
At a wave trough, the valve 200 shuts, the fourth two-way valve 238 opens, and the pressure in the fourth accumulator 222 is utilized to force the float under the water. As the fourth two-way valve 238 shuts, the third two-way valve 236 opens, and the pressure in the third accumulator 220 is utilized to force the float further under the water. Hereafter the third two-way valve 236 shuts, and the second two-way valve 234 opens, and the pressure in the second accumulator 218 is utilized to force the float even further under the water. Subsequently, the second two-way valve 234 shuts, and the first two-way valve 232 opens such that the pressure in the first accumulator 216 is used to force the float further under the surface of the water. Finally, the first two-way valve 232 shuts, and the pressure valve 178 opens.
It will thus be appreciated that at least a portion of the potential energy released as the float 124 moves vertically out of the wave from position 174 g to position 174 h (cf. the lower part of
There may be provided more than four accumulators 216, 218, 220 and 222. For example, there may be provided six, eight, ten, twelve, twenty or even more accumulators.
The total loss of energy i.e. the sum of the small triangles, is defined by the following formula:
Accordingly, the larger the number of step N, the smaller is the total loss of energy.
The effect of the accumulators discussed above in connection with